drm/amd/powerplay: Fix buffer overflows with mc_reg_address

Smatch warned about the following lines:
ci_set_mc_special_registers() error: buffer overflow 'table->mc_reg_address' 16 <= 16
tonga_set_mc_special_registers() error: buffer overflow 'table->mc_reg_address' 16 <= 16

Change the logic to check before access instead of after incrementing.
It's fine if j reaches max after we're done. This allows the last entry
of the array to be filled without an error message for example.
Changed some whitespace to clarify grouping.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Ernst Sjöstrand <ernstp@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>